1. Field of the Invention
The present invention relates generally to geospatial mapping systems, and in particular, to a method, apparatus, and article of manufacture for computing floodplain encroachments using a geospatial mapping system.
2. Description of the Related Art
A floodplain is a land area (usually adjacent to a stream or river) that is susceptible to being inundated (occasionally or periodically) by flood waters from any source. Due to the high value of land and structures built adjacent to a stream or river, it is desirable to maximize and develop in the floodplain area. A floodplain development that can obstruct flood flows, such as a fill/backfill, a bridge, or a building is referred to as an “encroachment”. Various federal agencies require the purchase of flood insurance (in floodplain areas) and regulate new development for encroachments. As part of the analysis for encroachments, such federal agencies require the use of the HEC-RAS (Hydrologic Engineering Centers River Analysis System) program, developed by the United States Army Corps of Engineers, that provides a computer model used to conduct a hydraulic study, that produces flood elevations, velocities and floodplain widths. The use of the HEC-RAS system is time consuming, labor intensive, and therefore fails to provide an efficient mechanism for analyzing floodplains and encroachments. To better understand the problems of the prior art, a more detailed explanation of floodplains and HEC-RAS is useful.
Referring to FIG. 1, a floodplain 100 includes a floodway 102 and flood fringe 104. The floodway 102 is the channel of a river or other watercourse and adjacent areas the cover flood flows. In other words, the floodway 102 is the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood (see description below) without cumulatively increasing the water-surface elevation by more than a designated height. The flood fringe 104 is the portion of the floodplain 100 lying outside of the floodway 102 (i.e., areas that are covered by the flood but do not experience a strong current).
Generally, no new development is permitted within a floodway 102 unless a licensed professional demonstrates that the proposed encroachment will not result in a rise in the 100-year flood (also known as the base flood) elevation more than a designated height (usually 1 foot). The 100-year/base flood is a flood having a 1% chance of being equaled or exceeded in any given year. The base flood is used by the NFIP (national flood insurance program) as the basis for mapping, insurance rating, and regulating new construction. FEMA (Federal Emergency Management Agency) is the agency that is responsible for the NFIP field work (including floodplain maps) and community coordination.
As can be seen in FIG. 1, encroachments 106 may be constructed on the flood fringe 104. However, as stated above, FEMA will often not permit the constructions of any encroachment unless an engineer using HEC-RAS can verify that it will not increase the flood elevation of the base flood more than a designated height (e.g., 1 foot).
Currently, FEMA utilizes paper-based maps as part of the analysis and to obtain measurements. Calculations are performed based on the paper based maps, and data is entered into the HEC-RAS user interface. The HEC-RAS user interface utilizes a HEC-RAS engine to process the input data and outputs data that can be used to determine whether the encroachment with the specified input data is acceptable. However, the paper-based maps are not georeferenced, not current, and must be modernized. Accordingly, FEMA is in the process of modernizing the current floodplain maps over the next five (5) years where the paper-based maps are being converted to digital maps. In addition, numerous engineering flood studies are going to be performed to update inadequate and inaccurate previous studies upon which the paper maps are based.
The studies used to determine the floodmaps examine the areas through which floodwater will flow which requires a determination of ground elevations and obstructions to flow (such as vegetation, buildings, bridges, and other development) for these areas. Accurate data on the channel geometry and changes in the floodplain are obtained from ground surveys, aerial photography, or topographic maps. A cross section is a graphical depiction of the stream/river and the floodplain at a particular point along the stream/river. Cross sections are taken at right angles to the flow of the stream/river. At each cross section, the engineer has accurate information on the size and geometry of the channel, the shape of the floodplain, and the changes in the elevation of the ground. Accordingly, when calculating the stream channel through a floodway and the base flood measurements, engineers must perform various calculations and enter data for each cross section into the HEC-RAS system.
The prior art process for utilizing HEC-RAS often requires the manual construction of HEC-RAS input data, the manual determination and entry of cross section geometry data, and an iterative trial and error method for computing floodplain encroachments. Alternative methods may provide for a more automated method for extracting and entering cross-section geometry (e.g., by exporting and importing data from a GIS [geographic information system] mapping system/river mapping) but still require the manual entry of data into HEC-RAS along with an iterative trial and error method for computing the floodplain encroachments. Further, even the alternative partially-automated systems are not integrated with HEC-RAS thereby requiring users to restart their entire mapping process if an error or undesirable results are output from HEC-RAS. Further, due to the lack of integration, once complete, the user must export any final computations/values back to the GIS system.
FIGS. 2-5 illustrate the prior art technique used to define and calculate encroachments. FIG. 2 is a mock up display of a river 200 having various cross sections 3500, 4350, 5650, 6350, 7200, 8000, and 9200. As stated above, engineers must make various manual measurements and determinations to utilize the cross sections in an encroachment analysis. The dashed line indicates the deepest part of the river channel where the water flows. A builder may desire to build encroachments (e.g., by backfilling) on an area of the floodplain (e.g., on the right side near cross section 4350, or on the left side near cross section 7200. As an encroachment is built, the area where the water can flow is reduced thereby increasing the height of the flow up and/or down the river channel. Accordingly, one must examine the entire river flow to determine how and whether an encroachment will affect the floodplain. As stated above, in general, FEMA guidelines provide that encroachments cannot cause the height of the floodway to increase more than one foot.
As described above, the user must first manually construct the HEC-RAS input data, and manually determine and enter the cross section geometry data which is input into HEC-RAS. Thereafter, the HEC-RAS floodplain encroachment computation procedure is based on calculating a natural profile (existing conditions geometry) as the first profile in a multiple profile run. A profile (also known as a discharge profile) represents the profile/graph that specifies the amount of water that passes a point in a given period of time. Other profiles must then be run, to simulate and calculate the change in the height of the floodway based on various encroachment options, as desired. Accordingly, before performing an encroachment analysis, the user must develop an accurate model of the existing river system.
The user then selects a desired profile and attempts to set various values. To compute the floodplain encroachments, an engineer would first define floodplain encroachment station locations (i.e., the distances along a stream where computations are performed) for each cross section of the river 200 using a desired profile. FIG. 3 illustrates a dialog window used to define the floodplain encroachment station locations for a single profile 302 in the prior art. As illustrated, thirteen (13) river stations 304 are defined and for each station 304. The different stations 304 may also be selected by specifying the river and reach in areas 312-314. Once a reach is selected, the user can enter a starting and ending river station in fields 316-318.
The user is also required to select a profile number 302 to work on (i.e., to perform an encroachment analysis on). It may be noted that HEC-RAS requires that each of the encroachment analysis steps described herein must be performed under a single discharge profile 302 at a time. However, the encroachment analysis is not performed on profile one (1) because profile 1 is the base profile that is used for comparison.
The next step is to enter the desired encroachment method 306 to be used for the currently selected profile 302. Once a method 306 is selected, the data entry boxes 308-310 that correspond to the selected method 306 will display below the method selection box 306. For the method 306, HEC-RAS contains five optional methods 306 for specifying the floodplain encroachments. In method 1, the user enters right and left encroachment stations. The final mapping of encroachment stations is performed using method 1. In method 2, the user enters a fixed top width. In method 3, the user specifies the percent reduction in conveyance. In method 4, the user specifies a target water surface increase. Methods 1 and 4 are FEMA's preferred methods for defining encroachment stations. In method 5, the user specifies a target water surface increase and a maximum change in energy. In FIG. 3, method 5 has been specified for all of the stations 304. In FIG. 3, two value boxes 306-308 are displayed for the target water surface increase, and the maximum change in energy. By pressing the “set selected range” button 320, all of the stations and values will fill in the table 322. After the data has been put into the table 322, the user can manually change the method and corresponding data values directly from the table 322.
The station, profile and data entry process is repeated for all of the different profiles for which the user wants to perform the encroachment analysis. Once all the profiles and data has been entered, the user may select the “OK” button to proceed to the next step. Again, the user can only view one discharge profile 302 at a time and due to the manual entry required, it is very easy to make a mistake and overwrite a value that should not be overwritten.
The next step in the process is to perform the floodplain encroachment computational analysis based on the data entered using the interface of FIG. 3. FIG. 4 is the graphical user interface used to perform the computational analysis in the prior art. The user simply selects the “compute” button 402 to perform the analysis.
Once computed, the next step is to review the analysis results which may include a review of the increase in computed water surface elevation, a review of the change in floodway top width, and/or a review of the change in flow velocity. A different interface must be used to display such results. FIG. 5 is a graphical user interface used to display the results for the user to review in the prior art. As can be seen in FIG. 5, the change (i.e., the delta) in the water surface elevation is displayed in column 502. As at least one of the values in column 502 is over the one (1) foot mark (i.e., 1.07), the process may need to be repeated. The developer can further increase the encroachment at the water stations where the delta value is under one (1) foot. In addition, column 504 displays the top width that should be (based on FEMA guidelines) fairly uniform across all of the stations/cross sections.
However, note that the other area of concern is that of the velocity which is not displayed in the user interface of FIG. 5 of the prior art. With respect to velocity, it is desirable (and may be required) to maintain a velocity of under 6 ft/sec. Instead, the user must proceed to a different screen to view the velocity information. Accordingly, it is desirable to view all three items—the change in water surface elevation, the top width, and the velocity. Some prior art techniques may provide a single screen to allow the user to view the top width, water surface change, as well as the velocity in a single screen. However, such a display is in a separate graphical user interface and fails to show the user what encroachment definitions were used to obtain the results displayed. Instead, the user must manually recall such information from memory if desired.
Once the results are viewed in FIG. 5, to modify the different values used, the engineer is required to return to the graphical user interface of FIG. 3, redefine each field as desired, select the compute button in the interface of FIG. 4, and reevaluate the results using the interface of FIG. 5. Further, he user must recall the values desired (as displayed in FIG. 5) and manually input such values into FIG. 3 (copy and paste commands are not available). Such entry must be repeated for each profile desired while attempting to recall from memory the desired settings for each river station and each profile. This process is repeated numerous times until the desired results are achieved. Further, in FIG. 5, the previously defined floodplain encroachment values/results cannot be and are not displayed. In other words, if the user forgets the values previously used (or forgets to manually store them), a set of computations may be repeated unnecessarily.
Once the final desired results are achieved, since HEC-RAS is not integrated with any GIS system, the user must export the results from HEC-RAS back to the GIS system and may need to further manipulate the data for compatibility purposes.
In view of the above, one can see that the user is required to manually enter data for analysis and many steps are required merely to start the analysis. The user is then required to switch back and forth between user interfaces and dialogs for analysis and manipulating data while also requiring the user to export and import data back and forth between GIS systems and HEC-RAS. Lastly, there is no mechanism to mark a computation as finished or unfinished. Such manual efforts significantly slows the floodplain encroachment analysis process and is very inefficient.
What is needed is a mechanism to integrate a GIS system with HEC-RAS, a system that allows the user to view prior values utilized in a floodplain encroachment analysis, and an easy-to-use interface for entering, modifying, and updating encroachment values.